A common type of safety binding, called a "toe binding for holding the front of the boot" ensures the safety of a skier by responding to excessive torsional forces on the leg of the skier by laterally pivoting and releasing the boot from the ski. In these types of bindings, the pivoting of the boot in a lateral direction is performed against the bias of an elastic mechanism whose bias is adjusted to a predetermined value.
These traditional lateral release type skis suffer certain disadvantages particularly when a fall due to lateral torsional stress is combined with stresses causing the skier to fall backwards. When this occurs, the front of the boot exerts an upward force on a sole gripping element of the binding disposed above the sole of the boot. This upward force generates interference frictional forces between the edge of the sole and the sole gripping element. These interference forces bias the jaw against lateral pivoting and release the boot. Thus, the total force necessary for lateral pivoting and release of the boot is greatly increased and the skier's leg suffers abnormal torsional forces which might result in the leg being broken.
In response to this problem, means for improving the release were sought. Safety ski bindings having sole gripping elements that are sensitive to upward biases caused by the front of the boot so as to lessen the resistance of the bindings to lateral release have been proposed. These bindings, called compensation bindings, provide the most constant bias against lateral pivoting regardless of the type of fall. Examples of some of these bindings are described in French Pat. Nos. 75 19 439, 77 09 363 and 78 12 741 of the applicant. The interference forces in these bindings is compensated for the use of a sensor comprising a sole gripping element which, when pulled upward by the boot, decreases the bias against lateral pivoting of the elastic mechanism.
Other examples of compensation bindings are described in French Pat. Nos. 75 37 908, 78 07 805, 79 14 484 and 80 06 365 of the applicant. These bindings include a jaw which holds the front of the boot and which is adapted to pivot around either one of two support lines converging at a point above the ski. In these bindings, the jaw does not decrease the bias of the elastic mechanism; rather compensation is accomplished by the movement of the jaw itself. Upward stress on the jaw has a component in the direction of lateral pivoting around one of the two lines of support, thereby creating a lateral motor force which is combined with other lateral stress on the jaw. This motor force counters the interference friction force, and in this way, compensation is achieved.
These known compensation bindings improved safety considerably. However they still suffer shortcomings because they do not ensure compensation for interference forces in the event of a backward fall, that is, when the front of the boot lifts up and exerts an upward force on the jaw holding the boot, and in the event of a forward fall, where the bottom of the sole is forced against the ski. In a forward fall a large force is directed downward towards the ski thereby creating a large frictional force between the bottom of the sole and the support surface of the sole. This friction biases the jaw against lateral release of the boot and lateral pivoting.
There have been many attempts to eliminate or to reduce as much as possible the friction between the front of the sole of the boot and the upper surface of the ski. It has been suggested that a sensor be placed under the front of the boot so as to act on the binding's elastic mechanism to adjust its bias, as described in French Pat. No. 71 22 859. This sensor compensates for the interference forces when it is biased by the front of the boot during a forward fall. It accomplishes this by reducing the elastic mechanism's release threshold value (i.e., the force above which the bias of the elastic mechanism will be overcome and the jaw will laterally pivot). However, such an apparatus is of a limited value because it only compensates for frictional forces during a forward fall. As a consequence, when torsional forces causing a lateral twisting of the leg and a fall are combined with forces causing a backward fall the resulting situation becomes very dangerous to the skier. Interference frictional forces are not compensated for, thereby increasing the threshold for lateral release of the boot to a dangerous level. If the torsional forces are high, the leg may be broken.
Thus there is a need for a binding which compensates for interference frictional forces which occur during a backward fall as well as a forward fall. There is also a need for a binding having a reliable adjustment of the lateral release threshold, regardless of the direction of the fall.